feat: add authenticated admin shell

apps/web/src/composables/useAuth.js

@@ -0,0 +1,37 @@
+import { computed, ref } from 'vue';
+
+import { getCurrentPrincipal, login, logout } from '@/services/auth-service.js';
+
+const principal = ref(null);
+const isLoading = ref(false);
+const error = ref(null);
+
+function csrfToken() {
+  return document.cookie.split('; ').find((value) => value.startsWith('pokemon_inventory_csrf='))?.split('=')[1] ?? '';
+}
+
+export function useAuth() {
+  const isAuthenticated = computed(() => Boolean(principal.value));
+
+  async function load() {
+    isLoading.value = true;
+    try { principal.value = await getCurrentPrincipal(); }
+    catch { principal.value = null; }
+    finally { isLoading.value = false; }
+  }
+
+  async function signIn(email, password) {
+    error.value = null;
+    isLoading.value = true;
+    try { await login(email, password); await load(); }
+    catch (requestError) { error.value = requestError; throw requestError; }
+    finally { isLoading.value = false; }
+  }
+
+  async function signOut() {
+    await logout(csrfToken());
+    principal.value = null;
+  }
+
+  return { principal, isAuthenticated, isLoading, error, load, signIn, signOut };
+}